The invention relates to a bearing sealing means of earth boring bits used in well drilling, the petroleum industry, geologic surveys and the like.
Because of limited space in bearings of earth boring bits, an O-ring has been used as a radial seal for such bearings due to its simple structure and safe property. Such radial seals for bearings of earth boring bits are described in U.S. Pat. No. 3,397,928. In general, clearances of bearings in earth boring bits are greater (usually 0.08 to 0.23 mm) since the working temperature of such bits is higher. However, the greater clearance brings unfavorable effects when O-rings are used as radial seals. Significant compressive deformation is required to fit with the eccentric rotation of a loaded cone, however this causes increased heat generation due to the sliding friction of the O-ring. If the temperature becomes too great, the O-ring can be permanently deformed. For these reasons, an O-ring made of rubber cannot be used, otherwise its working life will be shortened when the bit is operated at high speed.
Attempts have been made to improve the sealing structures of bearing in earth boring bits, however none have been satisfactory. For example, a sealing assembly is disclosed in U.S. Pat. No. 4,623,028, which comprises a static and softer O-ring, a dynamic and harder O-ring and a rigid supporting ring. A smaller compressive deformation is designed for the dynamic O-ring, while a greater compressive deformation is designed for the static to compensate the eccentric rotation of the cone. Due to this structure, the sealing assembly can be used at high operating speed. Unfortunately, use of the assembly was limited because of its complex structure and large volume. A floating seal for earth boring bits is disclosed in U.S. Pat. No. 4,428,687. The seal comprises a groove formed on the bearing shaft of a head section. A split supporting ring is located in the groove. An O-ring is provided in an annular space defined by sidewalls of the groove, the outer circumference of the supporting ring, and the circumferential surface of the shaft so that a seal structure comprising radial and axial seals is formed. After forming the axial seal on the sidewall of the groove, there is air in the floating clearance between the inner circumference of the supporting ring and the bottom of the groove; and the floating clearance has been closed. During drilling, the pressure of drilling liquid is much greater than that of air located in the floating clearance. This causes the O-ring to be pressed partially into the groove, and thus deforms the supporting ring. This will cause the seal to no longer function. In practice the technical solution of the above patent is not satisfactory.